1. Field of the Invention
The present invention relates to an optical print head and image forming apparatus.
2. Description of the Background Art
In an optical print head employing a solid writing system using an LED array or an organic electro luminescence (EL) array as a light source, the operating distance of the lens array is short and a gap between the light-emitting surface and the surface of an image bearing (photoconductor) drum is extremely small; i.e., 2-3 mm.
Consequently, toner and paper dust adhering to the surface of the image bearing drum and toner stirred up by a developing roller are scattered by the rotation of the drum and adhere to the light-emitting surface of the lens array.
If left alone, such attached materials block beams of light that scan the surface of the image bearing drum, thereby reducing the amount of light reaching the image bearing drum, which leads to a reduction in image density and uneven density (i.e., vertical streaks) in the output image, that is, degraded image quality.
Typically, the print head is constructed of a main part having a substrate on which a light source is mounted, a lens array, and a housing that holds these at their arranged positions, and a supporting member for installing the main part in the frame of an image forming apparatus.
The supporting member is configured to bring a cleaner into contact with the light-emitting surface of the lens array and move the cleaner in the main scanning direction while maintaining contact with the light-emitting surface of the lens array.
The cleaner typically has a pad made of unwoven fabric such as felt having a sheet form made by compressing animal hair.
Although effective, cleaning performance is not satisfactory when such a felt has a weak contact force.
Conversely, if the contact force is excessively strong, it prevents the cleaner from moving smoothly, resulting in uneven cleaning and in the worst case damage to the light-emitting surface.
Therefore, providing a predetermined constant contact force of the felt against the light-emitting surface of the lens array in the main scanning direction (moving direction) is required.
In addition, in the optical print head employing a solid writing system using an LED array or an organic electro luminescence (EL) array as a light source, the focal depth of the lens array is shallow.
Therefore, unless the lens array and the surface of the image bearing drum are positioned to within ±0.1 mm of their proper locations, the beam spot of the light beam directed onto and scanning the image bearing drum becomes blurred.
Therefore, the position of the optical print head is determined by having projections that abut the image bearing drum or the supporting member at both ends in the main scanning direction in order that the light-emitting surface of the lens array and the surface of the image bearing drum precisely maintain their relative positions.
Where such a cleaner is provided, the range of movement of the cleaner is limited to the area between the projections.
Therefore, depending on the positioning of the projections, there is no space for retraction of the cleaner during printing.
The problem can be solved by configuring matters so that the cleaner can be retracted outside the projections, but such an arrangement requires that contact between the projections and the image bearing drum or the supporting member be temporarily broken.
This is also true in a case in which structural factors such as the supporting member of image bearing drum prevent movement of the cleaner in the main scanning direction.
That is, it is necessary to clean the light-emitting surface after it is moved away and separated from the surface of the image bearing drum.
Japanese Patent Application Publication No. (JP-A) 2011-025631 describes a structure in which a cleaner to clean the light-emitting surface of the LED print head is reciprocatorily moved in the longitudinal direction of the LED print head by a driving mechanism having a screw shaft and a slider screwed thereto while the cleaner is sandwiched between the image bearing member and the light-emitting surface.
JP2007-072321-A describes a structure having a guiding device to move a cleaner from a retracted position situated at the outside of one end of the LED print head relative to the height direction of the light-emitting surface to contact the cleaner with the light-emitting surface and guide the cleaner to clean the light-emitting surface of the LED print head along the light-emitting surface.
JP2000-206854-A describes a structure having a process cartridge and a cleaner integrally provided thereto.
The process cartridge has at least one image forming unit and is detachably attachable to an image forming apparatus.
The cleaner contacts and cleans the light-emitting surface of an LED print head upon detachment and attachment of the process cartridge.
JP2001-175046-A describes a structure having an LED array head movable between a first position at which the image bearing member is distant from the LED array head with a predetermined distance and a second position at which the LED array head is moved away from the first position relative to the image bearing member.
In the structure described in JP2011-025631-A mentioned above, since the LED print head and the screw shaft are independent from each other and the cleaner moves by the slider screwed to the screw shaft, it is difficult to keep a constant contact pressure of the cleaner against the LED print head along the longitudinal direction, i.e., the main scanning direction of the LED print head.
In addition, in the structures described in JP2007-072321-A and JP2001-175046-A mentioned above, it is not highly secured that the cleaner moves in the state in which the light-emitting surface of the print head and the image bearing member are separated.